1. Field of the Invention
The present invention generally relates to the field of the semiconductor device, and more particularly, to high voltage and low voltage devices.
2. Description of the Prior Art
Generally, there exists a trend in the field of ultra large scale integration to integrate different types of electric devices. We will suffer some issues while integrating these devices, and we have to solve these problems.
If we apply the conventional silicide process to the integration process of high voltage and low voltage devices, silicide such as titanium silicide (TiSi.sub.2) will be produced on the source/drain region of the devices. The titanium silicide does not affect the low voltage device. However, the higher electric resist resulting from titanium silicide will reduce the current of the device, and will spoil the device.
Besides, if we apply the polycide process to integrate the high voltage and low voltage devices, the high voltage device will not be affected, but the feature of low voltage logic device will be spoiled. And more particularly, in such process, we cannot use the prior cell library any more.
Consequently, it is an important issue to integrate high voltage and low voltage devices. It is important that, in the integration process, we keep using the cell library established before, and maintain the function of the high voltage device.